Not at all. The behavior in Lion (inverted scroll movement, bouncy scroll edges) encourages the user to see themselves as actually touching and directly manipulating physical objects on the screen (cf iPad/iPhone). One such resultant user-behavior is "flicking" to quickly perform the scrolling action.

If this behavior is overloaded with a navigational function, the user now may very well accidentally invoke the navigation function with a flick and lose data (HTML form data for example.)

This is a genuine usability issue that needs to be addressed by Apple.